1. Field of the Invention
The present invention relates to support and positioning devices, called flexure suspensions, used in two axis actuators for optical recording heads.
2. Description of the Related Art
The present invention relates, in general, to optical reading devices used in optical disc storage systems. Information is stored in these devices in tracks on an information medium such as a disc. When information is read from the information medium, no physical contact exists between the information medium and the read head. Instead, information is transmitted by light whose source is generally a laser diode. This information can be supplied by a writing beam to affect a change in the information medium or can be supplied by a reading beam to detect data encoded on the information medium.
In optical disc memory systems, information may be written in a variety of ways. For example, data can be stored on the information carrier in the form of marks. This information medium is commonly referred to as a write once non-erasable medium since the marks are typically unalterable once formed and recorded by a melting process. These marks are small depressions which provide variation to the smooth blank surface of the disc. These small depressions alter the surface of the disc so that, when a reflected light beam is converted to an electrical signal by means of an optical pick-up, the electrical signal can be used to distinguish the smooth disc surface from the depressions.
Another method for writing data is magneto-optical recording. According to this method, a heat source such as a laser increases the temperature of the recording medium beyond a threshold temperature known as the Curie Point or the Curie Temperature. Above this temperature, ferromagnetic materials lose their magnetic properties including magnetization and polarization. Upon cooling, the random magnetic field at a specified data spot on the disc may be set to a definite direction by an external magnetic field. Data is stored at a precise location on the information storage medium by simultaneously generating the required external field while heating that location with a laser and then allowing the location to cool. Because the polarization of the material affects its optical characteristics, the data can be read by a reflected laser beam in much the same manner as discussed above. This data remains encoded on the information medium until a heat source generates a temperature above the Curie Temperature erasing the information.
In optical disc memory systems, reading and writing are often achieved using a single laser source functioning at two respective intensities. During either operations, light from the laser source passes through an objective lens which converges the light beam to a specific focal point on the information carrier. The objective lens is moveable in a first, "focus" (up-and-down) direction in order to "focus" the laser beam to a small selected spot of light on the information medium (e.g., a disc) to write or retrieve information, and in a second, "tracking" (side-to-side) direction, to position the beam over the exact center of a read/write track. During a write operation, light from a laser is focused on a spot to raise the temperature of the spot, and to thereby permit the spot to cool in an imposed magnetic field. During data retrieval, laser light is focused on the recording medium and is altered by the information of the data storage medium. This light is reflected off the disc, back through the objective lens, to a photodetector. It is therefore this reflected signal that transmits the recorded information. It is especially important that, when information is being written to or read from the memory, the objective lens, and the exiting focused beam, be precisely focused at the center of the correct track so that the information may be accurately written and retrieved.
In these systems, the position of the objective lens in the focus and tracking directions is adjusted by a pair of control systems. Actuators which support the objective lens convert position correction signals from the feedback control systems into movement of the objective lens. This feedback control is imperative since, without it, a light beam may not converge at a precise desired location on the information medium.
Efforts to miniaturize these read/write or read only systems and to store as much information as possible on a given information medium have been limited by the difficulties of precisely controlling the focus and tracking of the laser light. As will be appreciated, failure to focus the light on a small enough area of the medium will result in too large a portion of the medium being used to store a given amount of information, or in too broad of an area of the medium being "read." Likewise, the failure to precisely control the "tracking" of the laser light will result in the information being stored in the wrong location or in information from the wrong location being read. In particular, it is extremely difficult to permit the precisely controlled movement of the objective lens needed for the focusing and tracking of the laser light while preventing movement of the objective lens in other directions which distort the desired movement patterns of the objective lens.